Photoflash lamp and method of sealing same



y 25,1967 G. c. GAINER ET AL 3,332,257

PHOTOFLASH LAMP AND METHOD OF SEALING SAME Filed Dec. 21, 1965 FEGSC.

FIG5A.

INVENTORS Gordon C. Gainer and Russell M. Luck ATTORNEY United States Patent ABSTRACT OF THE DISCLOSURE A thermoplastic photofiash lamp of the chemical reac- .-tion type employing the flash type envelope itself to provide the seal in the base support for securing the filament mount therein. The end of the photofiash lamp envelope or tube is heated and forced to flow to fill its own open end thus sealing the filament mount and leadin conductors in the open end of the tube.

This invention relates to photofiash lamps and more particularly to a photofiash lamp of the plastic-envelope, chemical-reaction type and a method for sealing said lamp.

Most present commercial photofiash lamps employ a sealed glass envelope which encloses an oxygen atmosphere which is frequently at above atmospheric pressure and a combustible material such as zirconium magnesium or aluminum, shredded as foil. An electrically energized filament causes the foil to react with the oxygen atmosphere to produce the desired flash of light. In order to prevent rupture of the glass envelope when the lamp is fired, due to the sudden increase in pressure accompanying the flash, an organic lacquer coating is normally placed on the outside surface of the lamp envelope.

It has been found that from the standpoint of cost of manufacture and safety of operation the use of plastic photofiash lamp envelopes is highly desirable but impractical in conventional lamps since the plastic will not retain the oxygen atmosphere for an acceptable length of time. The use of a powdered metal and a solid chemical oxidizing agent as the flash producing material in a sealed plastic photofiash lamp envelope which has been sealed in, and encloses, an ambient atmosphere, of the type disclosed in the patent application of Norman P. Baird, Ser. No. 197,639, filed May 25, 1962, now Patent No. 3,220,224, for a Photoflash Lamp, and owned by the present assignee, solves many of these problems.

The press-type seal heretofore used through-out the lamp making industry, wherein the open end of a glass or plastic envelope is heated and laterally compressed or pinched, has not been wholly satisfactory when employed under the high-pressure, high-temperature conditions found in plastic lamps employing the powdered metal and solid chemical oxidizing agent mixture systems. This method can cause a reduction in envelope wall thickness in the envelope area adjacent the seal which results in a weakened area where rupture can occur. Such envelope rupture is apparently caused by a combination of the hot gases and the extremely hot inorganic residue produced by the chemical reaction which residue as particles are embedded in a random manner, while in a red to white hot condition, in and around the base end of the plastic tube or envelope. These particles which soften the plastic and combustion pressure from within the tube can cause the molten plastic to rupture as a very small hole at the thinner regions of the plastic enclosure. It will be apparent then that when the tube or envelope is sealed in the conventional manner, through lateral com- 3,332,257 Patented July 25, 1967 pression, the walls of the tube elongate near the edges of the seal thus providing thin walled sections in the area of the seal thereby enhancing the probability of rupture.

Accordingly, it is an object of the present invention to provide a plastic photofiash lamp which will neither fracture nor rupture under normal high-pressure, hightemperature operating conditions.

Another object of this invention is to provide a plastic photofiash lamp having a unitary body and end seal.

A further object of the present invention is to provide a method for quickly and economically sealing the end of a plastic photofiash lamp.

Yet another object of the present invention is to provide a method for sealing the end of a plastic photofiash lamp in a manner which will prevent any type of rupture or failure under the required high-pressure, high-temperature firing conditions.

The aforesaid objects of the invention and other objects which will become apparent as the description proceeds, are achieved by providing a photofiash lamp which includes a radiation-transmitting sealed plastic envelope having a flash-producing charge positioned therewithin and a filament mount including a primer charge sealed through one end of the plastic envelope by a thick boule of plastic. The thick boule is formed by placing the open end of the thermoplastic envelope in a flow directing mold, heating the envelope end, and applying suflicient compressive force axially of the envelope While directing the flow of the heated portion to cause the heated plastic material to flow toward and fill the open end of said envelope to form the thick boule (lump) around the lead-in conductors thus sealing the open end.

For a better understanding of the invention, reference should be had to the accompanying drawings, wherein:

FIGURE 1 is a perspective view of one preferred device for practicing the method of the present invention;

FIG. 2 is a sectional elevation view of the boule forming mold with a portion of a lamp tube in its inserted portion;

FIG. 3 is a sectional view of a photofiash lamp sealed in accordance with the present invention;

FIG. 4A is a sectional view of a photofiash lamp constructed in accordance with the present invention and having a plastic band around the sealed end thereof;

FIG. 4B is a sectional view of a photofiash lamp of the present invention having a metal sleeve secured therearound;

FIG. 5A is a sectional view of an embodiment of the photofiash lamp of the present invention including a plastic insert therewithin;

FIG. 5B is a sectional view of another embodiment of the photofiash lamp of the present invention having a plastic liner therewithin; and

FIG. 5C is still another embodiment of the photofiash lamp of the present invention including a plastic insert and glass liner therewithin.

Referring now in detail to the drawings wherein like reference characters represent like parts throughout the several views, there is shown in FIG. 1 a device capable of practicing the photofiash lamp sealing method contemplated by the present invention. This device or apparatus consists of a base 10 including a heating element 12 suitably placed in the center thereof and energized by any conventional means.

A pair of upright support members 14, 16 extend upwardly from the base 10 on opposite sides of heating element 12. A pair of guide members 18, 20 having arcuate end plates 19 and 21 are mounted at their other ends midway along upright members 14, 16 to loosely retain photofiash lamp tube 22 in a vertical position. A platen 24 is provided for applying a predetermined load axially of the photofiash lamp 22. As shown in FIG. 1,

platen 24 has a pair of apertures 25 for snugly but slidably receiving support members 14 and 16 and a pair of notches 26 through which may be applied suitable pressure to generate the necessary axial load to tube 22. A mold or a die 28 is situated on the heating element 12 and may be aluminum, Teflon or any other suitable material. As shown in FIG. 1, mold 28 is aluminum and of the split type having a Teflon coating on the inner surfaces of the mold cavity 29. Mold cavity 29 is generally cylindrical in its upper portion and tapers out at the bottom to a substantially shallow-pointed shape. A yoke 30 having a cross bar 32 and a tightening element 34 is adapted to secure the two halves of split mold 28 together. A thermocouple 36 is located within the split mold and adapted to register the temperature thereof on a meter (not shown). 'It should be understood that the mold may be of solid block construction since the Teflon coating permits easy withdrawal of the photoflash tube after the seal is formed.

In practicing the method of the present invention a plastic tube preferably of cellulose propionate, polycarbonate or polystyrene having a charge of powdered metal and solid chemical oxidizing agent mounted preferably near the closed end thereof, for example as at 38, is employed. First a filament mount 40 including a pair of leadin conductors 42, a glass bead 44 and a tungsten filament coated with an igniter material of powdered metal and solid chemical oxidizing agent 46 is located and secured in the center of split mold 28. Plastic tube 22 is then placed between the arcuate end plates 19 and 21 of the tube guide members 18 and 20 and the end portion 48 thereof placed around filament mount 40 in split mold 28 to the maximum depth permitted by mold cavity 29. The split mold 28, and consequently the lower portion 48 of plastic tube 22, are heated by heating element 12 at from 175 C. to 220 C., depending upon the thermoplastic material employed, for from about to 60 seconds depending again upon the composition of the mold and thermoplastic. After the plastic has reached a softened state, pressure of from 15 to 30 psi. is applied through platen 24 to the upper end of tube 22 for from about 30 to 45 seconds. The heat softened cylindrical plastic side walls of the tube at end 48 are forced under the pressure applied through platen 24 by the shallowpointed or rounded bottom portion of mold cavity 29 to flow into the center of tube 22 around the lead-in conductors 42 of filament mount 40. Tube 22 is thus consumed at its lower end and the material therefrom directed internally forming a thick plastic boule, sealing the end of tube 22 around lead-in conductors 42.

Basically then, the method of the present invention involves placing a filament mount within a mold cavity surrounding the filament mount within the mold cavity with the end of a plastic flash lamp tube, and heating the end of the flash lamp tube surrounding the filament mount until said end reaches a softened condition capable of deformation under slight pressure. Pressure is then applied axially of the tube to cause the lower end of the tube to deform and fill its own open end around the lead-in conductors of the filament mount to form a thick plastic seal.

Of course, many variations are possible insofar as the equipment for practicing the present invention is concerned. The mold may be heated by several obvious methods. The mold may be heated either electrically, by a separate heating element or by induction coils within the mold itself. Alternatively direct or indirect application of flame may be employed. The tube may be guided and retained in a vertical position within the mold by mechanical means, by hand, or otherwise and the pressure required to deform the softened plastic end of the tube may be applied by gripping the tube midway therealong and applying a downward force, or axially from the top as shown in FIG. 1, or the top of the tube 22 may be 4 held in a fixed position while the pressure is applied from beneath the base 10.

Various types of thermoplastic polymers have been successfully utilized in the sealing of photoflash lamps of the type contemplated by the present invention. Tubular cellulose propionate has been satisfactorily sealed by first preheating the mold from between 15 to 30 seconds when an aluminum mold is employed and from between 30 to 60 seconds with a Teflon mold at from between C. to C. and then applying a pressure of 15 to 30 pounds per square inch axially of the tube for from 30 to 45 seconds. For polycarbonate, temperature operation is 210 C. to 220 C. with similar pressure and time limitations.

FIG. 3 represents a cross-section of a photoflash lamp constructed by the present invention and includes an essentially optically clear radiation transmitting plastic tube 22 having a flash producing charge 38 positioned within one end thereof. This flash producing charge may comprise a mixture of a predetermined amount of finely divided, solid, oxygen-liberating substance and a predetermined amount of finely divided metallic substance, of which barium nitrate, strontium nitrate or potassium chlorate may comprise the oxidant and zirconium the metal. At the other end of the tube there is located a filament mount 40 including a pair of lead-in conductors 42, a glass bead 44, and a tungsten filament covered by a conventional primer charge 46. The lead-in conductors 42 of the filament mount 40 are sealed through the end of plastic envelope 22 in a thick plastic boule 50 which is formed from the cylindrical sides of plastic envelope 22. The filament mount 40 could alternatively be of the type disclosed in U.S. Patent 2,811,846 to Rively and employ only a single lead-in conductor with spark gap actuation of the primer material.

FIGS. 4A and 4B represent alternative embodiments of the photoflash lamp of FIG. 2. In FIG. 4A a plastic band or ring 52 is force fitted around the sealed end of photoflash tube 22 to provide increased strength in the area of the seal at the end of the tube where failure can occur upon firing of the photoflash lamp. In the FIG. 4B embodiment a metal ring, preferably a brass sleeve, is employed to reinforce the sealed end of the photoflash lamp. This brass sleeve 54 may be force fitted over the sealed end of the lamp tube, or it may be placed in the cavity 29 of mold 28 prior to sealing the tube and the tube then softened and the seal formed directly within the brass sleeve 54 with the additional attribute of a crimp type lock as the softened plastic hardness as at 56.

FIGS. 5A, 5B and 50 represent other alternative embodiments for the photoflash lamp of the present invention. In the FIG. 5A embodiment a plastic insert 58 is placed within the lower end of the photoflash tube 22, and as that end 48 is heated during the formation of the plastic boule 50 the insert 58, in addition to providing a reinforced wall area adjacent the igniter material, adds plastic material to the formation of the boule 50. The FIG. 5B embodiment employs a tubular plastic liner 60 throughout the entire lateral extent of the photoflash tube 22 to provide a reinforced surface for the photoflash lamp throughout its entire lateral extent and additionally contributes at the lower end 48 of the tube to the formation of plastic boule 50. Preferably, the plastic insert 58 and the plastic liner 60 are of the same material as the tube 22, but they may be of a different plastic material so long as the melting points are substantially the same.

The FIG. 5C embodiment adds lateral reinforcement to the entire side wall areas of photoflash lamp tube 22 with the addition of a glass liner 62 in combination with a plastic insert 58 thus providing the optical characteristics of glass in the area of maximum emission while still accommodating the shortening of the tube by deformation of plastic insert 58 during the heating and compressing process.

As can be seen by the foregoing, the present invention provides a photoflash lamp of the chemical mixture type which is tightly sealed by deformation of the lamp casing itself without any reduction in wall thickness, and which is not subject to fracture or failure during the firing of the lamp. It will be recognized that the present invention has achieved an improved photoflash lamp employing a novel sealing technique that may be easily and economically manufactured, is not subject to fracture or failure and is sealed from the mere plastic deformation of the lamp envelope itself.

While the best embodiments of the invention have been illustrated and described hereinbefore, it is to be particularly understood that the invention is not limited thereto or thereby.

What is claimed is:

1. A method for sealing a filament mount including lead-in conductor means within and through the open end of a sealed tubular plastic photoflash lamp envelope comprising the steps of:

(a) positioning said filament mount within the open end of said envelope with said lead-in conductor means extending externally thereof,

(b) positioning only that portion of said envelope adjacent the open end thereof within a flow directing mold,

(c) heating only the end of said envelope within said mold to a condition of plastic flow, and

(d) applying a compressive force axially of said tubular envelope while simultaneously directing internally unconstrained flow of said heated end of said envelope toward the interior thereof to form a thick globular seal around portions of said lead-in conductor means whereby upon cooling of said heated envelope end said filament mount is sealed in a fixed position within said tubular envelope with said leadin conductor means extending therefrom.

2. The method of sealing a filament mount as defined in claim 1 wherein said open end of said envelope is positioned within a crimped metallic sleeve positioned within said flow directing mold.

3. A method for sealing a filament mount including lead-in conductor means within and through the open end of a sealed tubular plastic photoflash lamp envelope comprising the steps of:

(a) positioning said filament mount within a flow directing mold,

(b) positioning only that portion of the open end of said envelope to be deformed within said mold to surround said filament mount with said lead-in conduct'or means extending externally of said envelope,

(c) heating the said portion of said envelope within said mold to a condition of plastic flow, and

(d) applying a compressive force axially of said tubular envelope while simultaneously deforming said heated portion of said envelope by directing internally unconstrained flow of said heated portion toward the interior thereof to form a thick globular seal around portions of said lead-in conductor means whereby upon cooling of said heated envelope end said filament mount is sealed in a fixed position within said tubular envelope with said lead-in conductor means extending therefrom.

References Cited UNITED STATES PATENTS 2,270,162 1/ 1942 De Margitta 6731 X 2,438,993 4/1948 De Boer 67-31 3,220,224 11/ 1965 Baird 67-31 JAMES W. WESTHAVER, Primary Examiner. 

1. A METHOD FOR SEALING A FILAMENT MOUNT INCLUDING LEAD-IN CONDUCTOR MEANS WITHIN AND THROUGH THE OPEN END OF A SEALED TUBULAR PLASTIC PHOTOFLASH LAMP ENVELOPE COMPRISING THE STEPS OF: (A) POSITIONING SAID FILAMENT MOUNT WITHIN THE OPEN END OF SAID ENVELOPE WITH SAID LEAD-IN CONDUCTOR MEANS EXTENDING EXTERNALLY THEREOF, (B) POSITIONING ONLY THAT PORTION OF SAID ENVELOPE ADJACENT THE OPEN END THEREOF WITHIN A FLOW DIRECTING MOLD, (C) HEATING ONLY THE END OF SAID ENVELOPE WITHIN SAID MOLD TO A CONDITION OF PLASTIC FLOW, AND (D) APPLYING A COMPRESSIVE FORCE AXIALLY OF SAID TUBULAR ENVELOPE WHILE SIMULTANEOUSLY DIRECTING INTERNALLY ENCONSTRAINED FLOW TO SAID HEATED END OF SAID ENVELOPE TOWARD THE INTERIOR THEREOF TO FORM A THICK GLOBULAR SEAL AROUND PORTIONS OF SAID LEAD-IN CONDUCTOR MEANS WHEREBY UPON COOLING OF SAID HEATED 